Electron beam coupling systems



2 Sheets-Sheet 1 LOAD OUTPUT TRANSFORMER INVENTOR 71 30 Z2 eri? oQaZ Ze/z" ATTORNEY Jan. 15, 1963 R. ADLER ELECTRON BEAM COUPLING SYSTEMS .2Sheets-Sheet 2 Filed Feb. 12, 1959 w! I a;

I/VI/E/VTOI? Roeri 0 25262 BY Mi ATTORNEY United States Patent ()fifice3,073,988 Patented Jan. 15, 1963 3,073,988 ELECTR-QN BEAM CGUPLINGSYSTEMS Robert Adler, Northfield, BL, assignor to Zenith RadioCorporation, a corporation of Delaware Filed Feb. 12, 1959, Ser. No.792,359 9 Claims. (Cl. 315-4) This invention relates to ElectronCoupling Systems. More particularly it has to do with systems fortransferring signal energy to or from electron beams. This applicationis a continuation-in-part of application Serial No. 738,546, filed May28, 1958, entitled Electronic Signal Amplifying Methods and Apparatus,and assigned to the same assignee as the present application.

In the aforesaid parent application there are disclosed a variety ofsignal amplifying devices. In general, these devices include an electronsource for projecting an electron beam along a predetermined pathterminating in a collector for the beam. Spaced along the beam pathbetween source and collector are several components including meansdisposed along a first portion of the path and responsive to appliedsignal energy for modulating the .beam. Next along the path toward thecollector are means for expanding the beam modulation after which signalenergy is extracted from the expanded beam modulation. The preferredforms disclosed in the parent ap .plication are those whichparametrically amplify electron signal motion. While the coupling systemof the present invention is suitable for use with a wide variety ofelectron beam signal amplifying apparatus, it is disclosed herein forpurposes of illustration as employed in the apparatus of the parentapplication and also as employed in the copending application of GlenWade, Serial No. 747,764, filed July 10, 1958, entitled ParametricAmplifier, and assigned to the same assignee as the present invention.

Although not restricted thereto, the coupling system of the presentinvention has especial value when utilized with high-gain low-noiseamplifiers and related devices.

One such device is the fast-wave parametric amplifier. In that device,gain is achieved by the use of a modulation expander which includesmeans for creating in the beam path a field establishing electronresonance for beam electrons, the electrons in addition being subjectedto a time variable inhomogeneous field. Cooperating with the expanderare input and output couplers for supplying energy to the beam andderiving amplified energy from the beam, respectively.

An amplification system such as the just-mentioned parametric amplifieris capable of amplifying signals over a wide range of frequencies. Inmany instances it is desirable to limit the range of frequenciessupplied to the beam in order to avoid amplifying undesired signals. Onthe other hand, in such cases it is usually desirable to accept andamplify a certain limited range of frequencies. One way of achievingthese ends is to employ a bandpass filter in the input coupling system.

In the process of amplifying signals in parametric and other types ofelectron beam amplification devices, signals are sometimes developed atother than the desired signal frequencies. As in the input couplingsystem, the output coupling system may likewise advantageously employ aband pass filter preferably centered upon the middle of the desired passband.

It is accordingly a general object of the present invention to provideapparatus for transferring signal energy between a signal device, suchas a source or load, and an electron beam while yet discriminatingagainst unwanted signal frequencies.

It is another object of the present invention to provide an electronbeam coupling system which is especially suitable for use withparametric amplifiers and the like.

A still further object of the present invention is to provide anelectron beam coupling system which acts as a wave filter whilerequiring a minimum number of physical components.

An electron beam coupling system constructed in ac cordance with thepresent invention serves as a filter for transferring signal energybetween a signal device and an electron beam traversing a predeterminedpath. The filter includes means for establishing resonance of electronsin the beam and means constituting a filter element coupled to the beam.The latter is coupled to the signal device by means including animpedance inverting network. This coupling system takes advantage of andutilizes the equivalent characteristics of the electron beam itself aspart of a combination of elements uniquely intercoupled to provide awave filter of desired characteristics.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The organizationand manner of operation of the invention, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description taken in connection with the accompanyingdrawings, in the several figures of which like reference numeralsidentify like elements and in which:

FIGURE 1 is a schematic diagram of one general form of apparatusembodying the present invention;

FIGURE 2 is a more detailed schematic diagram of electron beam couplingapparatus utilized in the embodiment shown in FIGURE 1;

FIGURE 3 is a simplified schematic diagram of the coupling apparatusshown in FIGURE 2;

, lines 9-9 in FIGURE 8.

In general, an electron-signal-motion expander is associated with meansfor modulating with signal energy an electron beam projected along areference path and means for demodulating the amplified signal motion.As illustrated in FIGURE 1, an electron beam is projected along areferencepath 10. The electron source for producing the beam may beentirely conventional and preferably includes the usual cathode togetherwith suitable focusing and accelerating electrodes for developing a welldefined beam of electrons. A collector may be disposed at the end of thepath remote from the electron source and may conventionally include ananode biased at a positive potential.

Disposed in a first portion of beam path 10 is a modulator 11 coupled toa signal source 12 by-means including an input transformer 13. Modulator11 is an electron coupler capable of imparting energy to the electronbeam in response to signal energy received from source 12. Whilemodulator 11 may take various forms it preferably includes means, suchas a magnetic or electrostatic field, for establishing an electronresonant frequency for beammodulation electron motion. A typical suchassembly, for transverse electron motion, includes a solenoidsurrounding the beam to establish lines of magnetic flux parallel to thebeam path and of a strength establishing a selected cyclotron frequencyfor electron motion. Modulation signals derived from source 12 andhaving a frequency similar to the cyclotron frequency cause theelectrons in the beam to orbit in an expanding helical path. Theamplitude of the modulation signal energy in this particular modulatoris represented in the beam by the radius of orbital motion as the beamleaves the modulator.

A variety of several known energy transfer mechanisms, including, forthe case of transverse motion, transmission lines and deflection platesspaced alongside the beam, may be utilized to modulate the beam withenergy from source 12. As illustrated, modulator 11 includes a pair ofdeflector plates 14 and located individually on opposite sides of beampath 18. As will be explained in more detail below, input transformer13- preferably includes means to match the impedance of source 12 tothat presented by deflectors 14 and 15.

To establish an electron resonant frequency approx imately equal to thesignal frequency along beam path 10, the space between electrodes 14 and15 is subjected to a magnetic field of a strength sufficient toestablish for electrons in the beam an electron resonance or cyclotronfrequency approximately equal to that of the source signal. To this end,deflectors 14 and 15 are placed within a solenoid indicatedschematically by the arrow H Following input modulator 11 and disposedalongside a second portion of beam path 10 beyond modulator 11 is anelectron modulation expander 16. On beyond expander 16 is a demodulator17 disposed alongside a third portion of beam path 10 and coupled by anoutput transformer 18 to a load 19. Demodulator 17 may for conveniencebe identical with modulator 11 although other appropriate electroncouplers may be utilized. As illustrated in FIGURE 1, demodulator 17therefore includes receptor electrodes 20 and 21 which preferably areidentical with electrodes 14 and I5.

The portion of the electron beam path disposed between electrodes 20 and21 is likewise subjected to a magnetic field of a strength to establishfor electrons in the beam a cyclotron frequency approximately equaltothe frequency of electron signal motion within the demodulator. As inmodulator 11, this field may be created by an ordinary solenoid coilencircling electrodes 20 and 21 as indicated by the arrow labeled H Asdiscussed in more detail in the parent application, the disclosure ofwhich is incorporated herein by reference, it is often convenient todispose the entire length of the apparatus within a single solenoidproducing a constant homogeneous magnetic field throughout the beampath. However, separate solenoids may be disposed when different fieldstrengths are required as when demodulator 17 is of a type of beaminteraction device different from modulator 11.

Load 19 is coupled to demodulator 17 through output transformer 18 in amanner similar to that for the coupling between source 12 and modulator11. Operation of demodulator 17 is the reverse of that of modulator 11.Motion of the electrons in the beam reacts with demodulator 17 totransfer energy from the beam to the demodulator from where it is fed toload 19.

In the disclosed apparatus it is preferred to remove energy components,at least those corresponding to the modulating mode eifected bymodulator 11, existing in the beam as it enters the modulator. Suchenergy components may constitute excess noise which otherwise would bepresent in the derived output signal. This noise is carried by theelectron beam and appears as energy components which are added to thesignal components; typical of such electron beam noise is thatoriginating in the electron source. Additional beam component energy mayalso be present in the form of other signals applied to the electronbeam prior to its passage through modulator 11. To the end of removingsuch signal component energy, modulator 11 is preferably constructed tointeract with the fast electron wave.

Two distinct electron waves can exist in an electron beam at a givenfrequency. As discussed in more detail in the aforesaid co-pendingparent application, the circuit wave may be either faster or slower thanthe beam. A simplified interpretation of the electron-wave action isdeveloped in the parent application by considering the electron beam assubject to a restoring force derived from the focusing field intransverse-field tubes and the space charge in longitudinal-field tubes.This restoring force enables each electron in the beam to oscillateabout its rest position in the beam at a frequency referred to as theplasma frequency in longitudinal-field tubes and as the previouslymentioned cyclotron frequency or transverse-resonant frequency intransverse-field tubes.

When the circuit wave is faster than the beam, the phase relationshipsbetween the circuit wave and the electron motions are such that when thesignal on the circuit augments the motion on the electron beam that samemotion has the effect of reducing the signal on the circuit and viceversa.

Therefore, by utilizing fast wave interaction at desired signal may betransferred to the beam while noise components are extracted therefrom.

In order then to take advantage of this fast electron wave or noiseabsorption phenomenon, for transversemode modulation the interactionelements of modulator 11 have an efiective electrical length along beampath 10' such that all fast wave energy components originally in thebeam are transferred to the modulator circuit while energy from signalsource 12 is transferred to the beam. To achieve this result, themodulator is loaded by a proper matching resistance. That is, source 12is matched to the beam through transformer 13 and modulator 14; with thebeam optimumly loaded, the noise is stripped therefrom. In consequence,the electron beam leaving input modulator 11 and traveling towardmodulation expander 16 contains energy corresponding to the signalenergy supplied by source 12 while containing but a minimum, if any,other fast wave energy such as that originally appearing on the beam inthe form of noise. Preferably, electrodes 14- and 15 also have aneffective electrical length equal to an integral multiple of the slowwavelength in order to minimize interaction with the slow electron wave.

In order to obtain useful gain, the modulation imposed upon the beam inmodulator 16 is expanded. That is, expander 16 produces amplification byimparting energy to the electron signal motion. The energy from whichgain is derived is supplied by an external source in a form whichpreferably minimizes the transfor to the beam of noise componentspresent in the external source, at least in the modulation mode to whichdemodulator 17 is responsive. With parametric amplification, the beamelectrons are subjected to an electron suspension or restoring-forcefield within expander 16 and the stiffness of the suspension isperiodically varied in phase with electron motion components so as toimpart energy to the electron motion. Briefly, this is achieved bysubjecting the electron beam to a time-varying inhomogeneous fieldduring its passage through modulation expander 16.

The theory of such parametric modulator expansion and a considerablymore detailed discussion of apparatus embodying these principles ispresented in the aforesaid parent application. The parent applicationalso discloses in more detail modulation expanders other than thoseemploying the principle of parametric amplification and with which thecoupling system of the present invention may advantageously be utilized.it is therefore unnecessary for the present to describe in any moredetail the nature of the apparatus and the operation of expander 16.Moreover, the electron beam coupling system of the present invention maybe utilized most advantageously with any of a large variety of electronbeam devices wherein signal energy appearing as motion of beam electronsis amplified. One example of such devices is the now conventionaltraveling wave tube; in the traveling wave tube, however, it is theslow-wave energy which is amplified as a result of which the couplingsystem does not coact with the electron beam to minimize noise in themanner described above. Nevertheless, useful application of the couplingsystem may be had in such devices in order to control and establish thepass-band of the signal channel.

The coupling system of the present invention is employed to transfersignal energy between a signal device and the electron beam. Thus, itmay be employed and associated with and as a part of either or both ofmodulator 11 and demodulator 17. For convenience of discussion, whenreference is made below to the electron coupler, it will be understoodthat either modulator 1 1 or demodulator 17 is intended. Whiledeflection plates 14 and 15 are illustrated and referred to in thediscussion of FIGURES 25 and signal source 12 is therein illustrated ascoupled to these deflectors, it will likewise be understood that thediscussion applies with equal force when receptors 20 and 21 aresubstituted for deflectors 14 and 15 and load 19 is substituted forsignal source 12 with output transformer 18 being identical to inputtransformer 13.

In accordance with the invention, the physical coupling elementsdisposed alongside beam path are intercoupled to constitute a filterelement coupled to the beam for which resonance of the electrons thereinhas been established. The invention resides in a recognition and use ofcertain characteristics of the electron beam itself, and more especiallyof the resonant electrons thereof. The coupling system devisedtransforms inductive and capacitive properties of the resonant beam andutilizes them as wave-filter elements. To these ends, an inductor 23 iscoupled between deflectors 14 and and is assigned a value which togetherwith the capacitance presented by the deflectors constitutes anantiresonant circuit tuned approximately to the frequency of signalsfrom source 12. The system further employs means, including an impedanceinverting network, coupling the beam-coupled means to the signal device,in this instance to source 12. Accordingly, anti-(resonant circuit 24,comprising inductor 23 and deflectors i4, 15 is coupled to one end of atransmission line 25 of an electrical length equal to one-quarter wavelength at the signal frequency. Line 25 is coupled at its other end,preferably by means to be described, to source 12. As is wellunderstood, per se, a quarter-wave transmission line serves to invertthe impedances at one end of the line as seen from its other end, and itis often referred to as a quarter-wave transformer.

According to a further aspect of the invention, line 25 is coupled tosource 12 through a second anti-resonant circuit 26 tuned approximatelyto the signal frequency. It is well understood by those skilled in theart that antiresonant circuits may take a variety of forms such ascavities resonant at the signal frequency, transmission lines similarlytuned and lumped combinations of an inductance and a capacitance havingvalues assigned to constitute a circuit parallel resonant at the signalfire quency. All of these devices may be schematically represented forease of understanding by such an inductance and capacitance. Hence,circuit 26 is illustrated in FIGURE 2 as comprising an inductor 27 and acapacitor 28.

Line 25 and signal source 12 are coupled to circuit 26 by suitable tapsalong inductor 27. Similarly, line 25 is at its other end tapped ontoinductor 23 of antiresonant circuit 24 which, although illustrated anddescribed in the form of lumped inductance and capacitive elements, maylikewise in different apparatus take the form of such otheranti-resonant devices as cavities and transmission lines; the latter,for example, are especially suitable for modulating and demodulating anelectron beam in which signal motion is represented by movement of theelectrons back and forth along the axis of beam movement as in theabove-mentioned longitudinal-field tubes employing space charge wavesand in which the electrons are resonantly suspended to have a plasmafrequency analogous to the cyclotron frequency of the device describedwith respect to FIGURE 1.

In order to properly match the impedance of signal source 12 to that ofimpedance inverting network and in turn to the electron coupler, thepositions of the taps on inductors 23 and 27 preferably are adjustableor at least are initially adjusted to achieve this end. In addition,anti-resonant circuit 26 preferably serves as a balance converter when,as in the present instance, source 12 is single-ended or unbalanced.

Since the achievement of impedance matching by adjusting such taps formsno part, per se, of the present invention, for convenience of furtherdiscussion FIGURE 3 illustrates the circuit of FIGURE 2 without theimpedance-matching taps, thus assuming that source 12 is so coupled andits impedance so adjusted that a proper match is obtained. Consequently,signal source 12 is shown as inductively coupled to circuit 26 through awinding 29. Otherwise, FIGURE 3 includes the same elements describedwith regard to FIGURE 2. It should be remembered, however, that whenfast-wave noise removal is contemplated, impedance matching must beoptimized to fully load the electron beam at the frequency orfrequencies for which noise stripping is to be had.

The characteristics presented by the resonant electrons of the beam maybe represented by the series combination of an inductance 30, acapacitance 31 and a resistance 32 coupled across resonant circuit 24,as depicted in FIGURE 4 wherein circuit 24 is represented by a capacitor14, 1S shunting inductor 23. Signal source 12 is depicted in FIGURE 4 asincluding a resistance 33 representing the internal source resistance.Thus, FTGURE 4 illustrates schematically the complete coupling system ofthe present invention including the resonant electron beam representedby elements 3ll32, anti-resonant circuit 24, quarterwave transformer 25and anti-resonant circuit 26, source 12 being coupled across the latter.

Quarter-wave transformer 25 has such properties that it inverts theimpedances presented by resonant circuit 24 and the electron beam asseen by source 12. That is, as depicted in FIGURE 5, source 12 ispresented first by antiresonant circuit 26 following which it sees theseries combination of an inductor 14, 15 and a capacitor 23, theinverted impedances of capacitor 14, 15 and inductor 23. Beyond thelatter series combination, source 12 sees the shunt combination of aninductor 31 and a capacitor 30 corresponding to the actual eifectiveseries combination of inductor 3t) and capacitor 31 shown in FIGURE 4.Finally, resistance 32, the load resistance of the beam, appears inshunt across the parallel combination of inverted inductance 31 andcapacitance 30. Whereas circuit 24 is actuality is anti-resonant at thesignal frequency, it appears to the source as a series resonant circuittuned to the signal frequency. Similarly, the actual effective seriescircuit of inductance 3t and capacitance 31, series resonant at thesignal frequency, appears to source 1?. as an anti-resonant circuitcomprising inductance 31 and capacitance 30.

The schematic diagram of FIGURE 5 will immediately be recognized asconstituting a pi-section wave filter including two shunt arms on eitherside of a series arm, all arms being tuned to resonance at the signalfrequency. The wave filter presents to the source a well-definedpassband centered about the signal frequency. Thus, the inventionproduces one arm of the filter without the necessity of providing actualphysical components therefor by taking advantage of the characteristicsof the resonant electron beam through a unique arrangement andassociation of the other components of the filter. The filter may bedesigned to have a particular pass band, eliminating serves as asuppressor electrode.

7 transfer of energy at all other frequencies. For example, when in usewith a parametric amplifier it may advantageously have a width justsufiicient to transfer energy at the signal and idler frequencies.

As a further example of the practical application of the invention,FIGURES 6 and 7 depict another form of parametric amplifier employingthe principles described in the aforementioned parent application andwhich form is specifically described in the aforesaid copendingapplication of Glen Wade. The entire assembly of this de vice isdisposed longitudinally within an elongated evacuated envelope 100through the opposite ends 101 and 102 of which suitable electricalconnecting leads project. Disposed near end 192 is an electron gunassembly 103. The electron gun includes a tubular cathode 104 supportedby a ceramic water 105 from a metal annulus 106 through which an end ofcathode 104 freely projects and on which end a cap is disposed andexteriorly coated with an electron emissive material 167 which whenheated by heater 103 emits electrodes outwardly therefrom. Spaced beyondcathode 104 is another metallic annulus 110 forrning with annulus 106 acage substantially confining cathode 104 except for the exposed coating107. Spaced in front of emissive coating 107 is a metallic wafer 109having an aperture aligned with the axis of cathode 104 and beam path tolimit and define the width of an electron beam projected through theaperture. Next beyond wafer 109 is an accelerator electrode 111 in theform of a metal disc also having an aperture centered on beam path 10 toaccept and pass the electron beam. Successively spaced beyondaccelerator 111 are first and second focusing electrodes 112 and 113likewise having respective apertures centered on beam path 10 andserving in operation to properly form the beam so that it emerges fromthe electron beam assembly traveling in a direction parallel to beampath 10.

Just beyond electron gun 103 is modulator 11, the electrodeconfiguration of which is shown more clearly in FIGURE 7. In modulator11 deflectors 14 and are formed of individually outwardly facing channelmembers spaced on opposite sides of the beam path. Inductor 23 iscoupled across the deflectors and transmission line 25 is tapped acrossintermediate turns of inductor 23.

In the next portion of the beam path outwardly from electrode beam gun103 is expander 16. the expander is a quadrupole composed of foursymmetrical generally hyperbolically shaped electrodes 120 each havingportions facing beam path 10 and outwardly projecting terminal portionsprojecting away from the beam path and across respectively adjacent onesof which inductors 123 are individually coupled to tune the quadrupoleto a frequency of twice the cyclotron frequency established by themagnetic field in which the device is placed during operation. Asuitable connecting lead (not shown) is connected to the mid-point ofone of the inductors to permit the application of a DC. potential to thequadrupole. A conductive loop is coiled coaxially around another one ofinductors 123 for feeding energy from the external signal source to thequadrupole. Preferably, opposite ones of the quadrupole electrodes arestrapped together to enforce operation in the pi mode.

On beyond expander 16 is demodulator 17 which as illustrated isidentical in construction with modulator 11. Accordingly, receptors and2 1 are disposed on opposite sides of the beam path and the load iscoupled to the receptors by means of a transmission line in a mannersimilar to that shown in FIGURE 7. Just beyond demodulator 17 is anapertured electrode 133 with its aperture centered on beam path 10 andwhich during operation Finally, the electron beam is collected by ananode 13 4 disposed transversely of beam path 10 beyond the aperture insuppressor 133.

The entire assembly is supported within envelope 100 by menas of fourceramic rods 136 symmetrically disposed about beam path 10 and extendingthroughout all In this instance,

of the various electrodes and through suitable insulating discs 137 inwhich the modulator, expander and demodulator electrodes are secured.The various dillerent electrodes are separated by suitable ceramicwashers as at 138 encircling ceramic rods 136 between the differentelectrodes; discs 137 are separated by similar ceramic sleeves as at139. The entire assembly is held tightly together by means ofcompression springs 14% acting between a collector mounting plate 141and a washer 142 pinned to ceramic rods 136. Of course, suitableinternal leads are brought out from the various electrodes to theterminals projecting through the base presses. While a ila-t press isshown in end 102, it is preferred to use a round button as in end 101 inorder to reduce interle'ad capacitance.

In a successfully operated amplifier constructed as illustrated inFIGURES 6 and 7, electron gun 103 includes a cathode emitting electronsat a current density of about ma./cm. perhaps 99% of which isintercepted by current control element 109. The apertured discssuccessively spaced in front of the cathode are energized at respectivepotentials of about 9, 150, 15 and 7 volts positive with respect to thecathode. By slightly varying the relative potentials it is possible toobtain a beam having characteristics resembling Brillouin flow.

The deflectors and receptors respectively in the modulator anddemodulator are spaced apart 0.030 inch and the intermediate portions ofthe expander electrodes facing the beam form a square 0.080 inch on eachside. In order that the expander acts on at least four orbits of signalmotion to obtain substantial gain, the length of electrodes is 0.400inch, the same as the length of the modulator and demodulatorelectrodes. The apertures in the support washers 137 have a diameter of0.100 inch. The entire structure is sealed within an envelope one inchin diameter.

In operation, the input and output couplers are tuned to 560 megacyclesby coils, such as coil 23 in the modulator, having about nine turnseach. The effective capacity of these resonators in the modulator anddemodulator is found to be less than one mmfd. and their unloaded Q isabout 250. The quarterwave transformers, such as line 25, areconstructed of 300 ohm transmission lines matched to the couplers whichpresent an impedance of about 8,000 ohms at 40 microamps beam current;so loaded the effective Q is about 20. Coils 123 tune the quadrupole to1120 megacycles, the frequency of the driving signal source coupledthereto.

The tube is placed within a homogeneous magnetic field adjustable topermit variation above and below a strength of approximately 200 gauss.It has been found in operation that the DC. potential applied to thecouplers of the modulator and demodulator has no critical in. fluence onperformance; it is approximately six volts. The DC. potential applied tothe quadrupole has been found to be somewhat more critical and ingeneral is of a value of between 4 and 7 volts. The collector voltage is200 volts, tall voltages discussed being positive with respect to thecathode.

While, as discussed above, anti-resonant circuit 26 may take a varietyof forms, a practical mechanical assembly is illustrated in FIGURES 8and 9. The assembly includes a cylindrical metal housing Shaclosed atone end by a metallic wafer 51 having two cylindrical openings 52communicating with the interior of housing 50. Spaced from wafer 51within housing 50 is a wafer 53 of insulating material having a pair ofapertures 54 aligned with apertures 52. Extending through, between and ashort distance beyond the mutually remote faces of wafers 51 and 53 area pair of hollow metallic cylinders 56, the latter having mutuallyfacing narrow slots 57 located within housing 50 near wafer 51. Disposedwithin cylinders '56 and projecting through water 51 are a pair ofmetallic tubes 58 bridged across their ends exterior of housing 50 by ametallic disc 59. A coaxial cable 60, for connection to signal source 12at its remote end (not shown), is coupled to tubes 58. Its outerconductor or braid 61 is electrically connected as by soldering to disc59. Its inner conductor 62, encased within an insulating sleeve 63, isled through one tube 58 and terminates at a position adjacent the slot57 therein. The terminal end of conductor 62 is electrically connectedby a strap 65 to the other tube 58.

Projecting through wafer 53 and slideably disposed within cylinders 56are a pair of metallic rods 67 bridged at their outward ends by aninsulating block 6%. Projecting on outwardly of housing 50 for ease ofmoving rods 67 in and out of cylinders 56 is a rod 69* of insulatingmaterial. Electrically coupled to the outward ends of rods 67 andprojecting alongside each rod on the mutually facing sides thereof are apair of metallic plates 70.

Slideably telescoping over the exterior surface of housing 59 is asleeve '72. Sleeve 72 carries a block 73, affixed to the sleeve byscrews 74, projecting through and sliding in a rectangular slot 75 cutlongitudinally in housing 50. Extending through an opening 77 in sleeve72 and through block 73 are a pair of wire leads 78. Slot 77 is locatedsymmetrically with respect to cylinders 56 to individually position theinner end portions of leads 78 in frictional contact with cylinders 56.

It will be observed that movement of rods 67 in and out of housing 50'varies the effective electrical length as well as the actual mechanicallength of a transmission line matching section composed of rods 67,cylinders 56 and metallic washer 51. Plates '76 present additionalcapacitance in the line, having the effect of rendering it electricallylonger. In electrical effect, this transmission line section representsanti-resonant circuit 26 the operation of which was explained above indetail with regard to FIGURES 2 through 5. It may be tuned to thedesired signal frequency by movement of rods 67 in or out of cylinders56.

By varying the amount by which tubes 58 project within cylinders 56, thedistance between inter-coupling strap 65 and disc 51 is varied to permitadjustment of the impedance match between cable 6%} from source 12 andthe transmission line section forming circuit 26. This is shownschematically in FIGURE 2 by the adjustable tap in the coupling circuitbetween source 12 and inductor 27.

Line 25 (of FIGURE 2) is coupled to the transmission line section byslider leads 78. Movement of leads 78 relative to cylinder 56 serves tovary the match between line 25 and modulator If by permitting connectionbetween line 25 and the transmission line section at a point oncylinders 56 of the latter presenting the proper matching impedance. Theoutput as taken by sliding leads 78 is balanced. The input as presentedby cable 61 is unbalanced. However, the input coupling system includingrods 58, inner conductor 62 and strap 65 serves as a balance converterto properly couple the unbalanced input to the balanced output.

Quarter-wave transformer 25 serves an additional purpose, one arisingfrom practical necessity perhaps but yet one which is satisfied withoutadditional components. Of course, signal source 12 is located externallyof the envelope enclosing the amplifier. While certain of the elementsdescribed including line 25 and anti-resonant circuit 26 may beincorporated entirely within the envelope housing the electron beamdevice, it is more convenient to the end of permitting adjustment of thevarious taps for impedance matching purposes to locate at least part ofthe structure externally to the device. At the same time, it is mostconvenient to pass a simple transmission line through a seal in theevacuated device for external connection. Thus, from a practicalstandpoint it is usually desirable to include a length of transmissionline between the electron couplers and a point located externally of theevacuated enclosure. The system of the present invention takes advantageof such a line and assigns to it an effective quarter-wavelength at thesignal frequency so that not only does it serve to feed energy into orout of the evacuated enclosure but it also functions as an essentialpart of the coupler system. Thus, part of quarter-wave transformer 25may be included within envelope 5%? and another part externally thereof.

It is well understood by the art that the expression effectiveelectrical length includes proper multiples of the basic length. Forexample, the length of quarterwave transformer 25 may actually beone-quarter wavelength at the signal frequency or may be increased bythe addition of any number of half wavelengths thereto.

It has been pointed out that the coupling system of the presentinvention may be used as part of and in cooperation with many differentvarieties of electron beam apparatus. It is essentially directed to acombination including modulator elements coupled to a beam the electronsof which exhibit resonance. Preferably, the system is one which coactswith an electron beam device for amplifying fast electron beam energywhereby noise on the beam may be removed. The system is advantageouslyemployed both in modulation and in demodulation to impress energy uponan electron beam and to derive energy therefrom, respectively. Itsutility lies principally in the creation of a coupling system which notonly serves to properly transfer energy between the beam and a signaldevice but which also serves as a wave filter without the requirement ofphysically including all of the elements or components electricallynecessary to com plete the filter structure. Moreover, the componentswhich are physically employed generally serve other functions inaddition to that of constituting parts of the wave filter with resultingeconomy and compactness. The practical mechanical embodiments discussedand described present the additional advantage of simplicity ofadjustment and ease of manufacture.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theinvention in its broader aspects. Accordingly, the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

I claim:

1. A filter for transferring signal energy of predetermined frequencybetween a signal device and an electron beam comprising: means forprojecting said beam along a predetermined path; means for renderingsaid electron beam resonant at said frequency; a filter elementcomprising a circuit resonant at said frequency coupled to said resonantelectron beam; and means, including an impedance inverting network,coupling said filter element to said signal device.

2. A filter for transferring si nal energy of predetermined frequencybetween a signal device and an electron beam comprising: means forprojecting said beam along a predetermined path; means for renderingsaid electron beam resonant at said frequency; a filter element,comprising a circuit anti-resonant at said frequency, coupled to saidresonant electron beam and means, including a signal translating deviceconstituting a quarter-wave transformer at said frequency, coupling saidfilter element to said signal device.

3. A filter for transferring energy of predetermined frequency between asignal device and an electron beam comprising: means for projecting saidbeam along a predetermined path; means for rendering said electron beamresonant at said frequency; a filter element comprising a circuitanti-resonant at said frequency coupled to said resonant electron beam;a filter member comprising a circuit anti-resonant at said frequencycoupled to said signal device; and an impedance inverting networkcoupling said element to said member.

4. A bandpass filter centered on a predetermined frequency fortransferring signal energy of said frequency between a signal device andan electron beam comprising: means for projecting said beam along apredetermined path; means for rendering said electron beam resonant atsaid frequency; a filter element comprising an antiresonant circuittuned to said frequency and coupled to said resonant electron beam; afilter'member comprising an anti-resonant circuit tuned ,to saidfrequency and coupled to said signal device; and means, including aquarterwave transformer at said frequency, coupling said element to saidmember.

5. In apparatus for transferring signal energy of predeterminedfrequency between a signal device and an electron'beam, a filtercomprising: means for projecting said beam along a predetermined path; apair of conductive plates disposed on opposite sides of said path; an inductor coupled between said plates with said inductor and said pair ofconductive plates together being anti-resonant at said frequency; acircuit anti-resonant at said frequency; and an impedance invertingnetwork coupling said anti-resonant circuit to said inductor.

7. A filter for transferring signal energy of predetermined frequencybetween a signal device and an electron beam comprising: means forprojecting said beam along a a predetermined path; means for renderingsaid electron beam resonant at said frequency; a filter element,comprising a circuit anti-resonant at said frequency, coupled andimpedance-matched to said resonant electron beam;

1 2 and means, including a signal translating device constituting aquarter-Wave transformer at said frequency, coupling and impedancematching said filter element to said device.

8. A filter for transferring signal energy of predetermined frequencybetween a signal device and an electron beam comprising: means forprojecting said beam along a predetermined path; means for renderingsaid electron beam resonant at said predetermined frequency; a filterelement comprising a circuit resonant at said frequency coupled to saidresonant electron beam; means, including an impedance inverting network,coupling said filter element to said signal device; and means forestablishing optimum impedance match of said signal device through saidnetwork and element to said beam.

9. A filter for transferring energy of predetermined frequency between asignal device and an electron beam comprising: means for projecting saidbeam along a predetermined path; means for rendering said electron beamresonant, at said predetermined frequency; a filter element comprising acircuit resonant at said predetermined frequency coupled andimpedance-matched to said resonant electron beam; a filter membercomprising a circuit resonant at said predetermined frequency coupledand impedance-matched to said signal device; and an impedance invertingnetwork coupling and impedance matching said element to said member.

References Cited in the file of this patent UNITED STATES PATENTS2,879,439 Townes Mar. 24, 1959 OTHER REFERENCES Microwave TransmissionCircuits, by G. L. Ragan, Radiation Lab. Series, vol. 9, pages 667 to683, published by McGraw-Hill, 1948.

Article by Louisell and Quate, pages 701-716, Proc. of I.R.E., April1958.

1. A FILTER FOR TRANSFERRING SIGNAL ENERGY OF PREDETERMINED FREQUENCYBETWEEN A SIGNAL DEVICE AND AN ELECTRON BEAM COMPRISING: MEANS FORPROJECTING SAID BEAM ALONG A PREDETERMINED PATH; MEANS FOR RENDERINGSAID ELECTRON BEAM RESONANT AT SAID FREQUENCY; A FILTER ELEMENTCOMPRISING A CIRCUIT RESONANT AT SAID FREQUENCY COUPLED TO SAID RESONANTELECTRON BEAM; AND MEANS, INCLUDING AN IMPEDANCE INVERTING NETWORK,COUPLING SAID FILTER ELEMENT TO SAID SIGNAL DEVICE.